The invention relates to a semiconductor device comprising a semiconductor body provided with a superlattice which alternately comprises layers of an indirect semiconductor material A.sup.III -B.sup.V and layers of a mixed crystal (alloy) of the same material in which one of the elements A and B is replaced in part by an equivalent element C, the superlattice exhibiting at least in a direction at right angles to the interfaces between the layers a direct band transition due to zone folding.
As is known, the term "direct transition" is used when in the K space the minimum of the conduction band lies above the maximum of the valence band (.GAMMA. point). When these extreme values are relatively displaced, the transition is indirect. Direct transitions are more particularly (but not exclusively) of importance for semiconductor lasers. In the case of a direct transition, the interaction electron--photon is a two-particle problem, as a result of which the transition probability of the transition of an electron from a high to a low level is comparatively high. In the case of an indirect transition, this transition probability is determined by a three-particle interaction (electron--photon--phonon) and is consequently generally so low that materials having such a transition cannot be used for lasers.
The most generally known and most frequently used semiconductor material for lasers is GaAs, which exhibits a direct transition. In the case of a band gap of 1.42 eV, radiation in the infrared is emitted by the GaAs. However, radiation of a shorter wavelength is desirable for many applications. When a fraction X of the Ga is replaced by Al, it is possible to reduce in GaAs the wavelength down to the red (nearly infrared) range. Since the fraction X is bounded by a limit value (0.45), above which the material exhibits an indirect band transition, such as pure AlAs, this method is not suitable to obtain small wavelengths. AlAs has in itself a suitable band gap (2 eV, corresponding to .lambda..apprxeq.590 nm in vacuo), but has an indirect band transition.
In the article "A GaAs.sub.x P.sub.1-x /GaP strained layer superlattice" by G. C. Osbourn et al in Appl. Phys. Lett. 41 (2), July 15, 1982, pages 172/174, there is described a superlattice alternately comprising 60 nm thick layers of GaAs.sub.x P.sub.1-x and 60 nm thick layers of GaP, which materials are both indirect in themselves. Due to the superlattice configuration, a direct transition can be obtained by zone folding, as indicated in the aforementioned publication. The aforementioned materials are chosen so that due to the difference in lattice constants and the strain in the crystal lattice caused thereby, variations occur in the energy bands. Such a configuration has the disadvantage that both during and after the epitaxial growth of the layers defects are liable to be introduced into the crystal lattice.